Goals for the period June 1, 1980 to May 31, 1981, are as follows: 1) to conduct further studies on hypophysectomized rats to determine the relationship between testoterone levels and sperm production; 2) to complete ongoing studies on testicular vein-rete transfer of testosterone; 3) to continue investigation into estrogen in the rete fluid and the effect of gonadotrophins and other factors upon men; 4) to examine the influence of temperature upon rete fluid flow, sperm and testosterone concentration; 5) to measure the rate and characteristics of transport of steroids and particulates along the seminiferous tubule.